1. Field of the Invention
The present invention relates to a bisimide compound, a polyimide resin composition comprising the bisimide compound, and a carbon fiber reinforced polyimide composition comprising a carbon fiber coated on the surface with the bisimide compound.
2. Description of the Related Art
Materials having more excellent high-temperature characteristics have recently been required in order to enhance performance and reduce weight on various industrial materials in the fields of electric and electronic devices, space and aeronautical equipment and transport machinery. In these materials, polyimide has mechanical strength, dimensional stability, flame retardance and electrical insulation properties in addition to its excellent high-temperature resistance, and has hence been widely used in the above industrial fields. Polyimide of high molecular weight, however, generally has a high softening point and is insoluble in almost organic solvents. As a result, many difficulties have been encountered for the use of polyimide.
ULTEM(Trade mark of General Electric Co.), a representative thermoplastic polyimide resin, has superior heat resistance and mechanical strength compared to general purpose engineering plastics. Consequently, it is called a super engineering plastic and widely investigated for use in electric and electronic devices, machines and automobiles.
Accompanied with the recent progress of technology, it has been demanded to develop a novel thermoplastic polyimide resin having heat-resistance and mechanical characteristics which are superior to ULTEM.
For example, U.S. Pat. No. 4,847,349 discloses a process for preparing polyimide resin by reacting etherdiamine with tetracarboxylic acid dianhydride. Japanese Laid-Open Patent Hei 2-018419 proposes a process for preparing polyimide resin by reacting 3,3'-diaminobenzophenone and tetracarboxylic acid dianhydride. Both patents have provided novel polyimides having heat resistance and mechanical characteristics which are superior to conventional polyimide.
The above polyimides are much superior in heat resistance and other characteristics to common engineering plastics represented by polyethylene terephthalate, polybutylene terephthalate, polyether sulfone, polysulfone and polyphenylene sulfide. However, increased molecular weight lowers melt flowability and melt processability of the polyimide is still inferior to these engineering plastics.
In order to enhance the characteristics of polyimide resin, mechanical strength in particular, fibrous reinforcement, particularly carbon fiber, is generally incorporated.
Carbon fiber is frequently used for carbon fiber reinforced plastics which use epoxy resin as a matrix and hence epoxy resin is commonly used for the collecting agent of carbon fiber. As a result, the epoxy resin collecting agent is effective when thermosetting resin such as epoxy resin is used for the matrix. However, epoxy a resin has poor adhesion to polyimide resin and resin composition having good mechanical strength cannot be obtained.
A process of using polyimide resin for the collecting agent of carbon fiber has been disclosed, for example, in Japanese Laid-Open Patent Sho 53-106752. However, polyimide resin must be generally processed at temperatures higher than 300.degree. C. and the collecting agent decomposes by heat in the processing step to cause problems such as formation of voids and reduction of weld strength. Further, Japanese Laid-Open Patent Sho 56-120730 describes a process for using a carbon fiber collected with aromatic polysulfone resin. However, the process leads to merely a small increase in mechanical strengths and has not yet fully satisfied desired characteristics.
An object of the invention is to provide a compound having outstanding processability in addition to excellent heat resistance.
Another object of the invention is to provide a processable polyimide-based resin composition having very excellent melt flowability without impairing the essential characteristics of polyimide.
A further object of the present invention is to provide a polyimide-based resin composition having excellent mechanical strengths.